A tyrosine kinase with Ig and EGF homology domains 2 (Tie2) is a receptor type tyrosine kinase. Tie2 is mainly known to be expressed in vascular endothelial cells. As the ligand, Angiopoietin-1 (Ang-1) and Angiopoietin-2 (Ang-2), which are multimer type secreted glycoproteins, are known.
Ang-1 functions as an agonist for Tie2. It has been found that when Tie2 binds to Ang-1, it is autophosphorylated by forming a multimer and transmits a signal into a cell, thereby promoting an anti-apoptotic action of vascular endothelial cells, vascular stabilization via a permeation inhibitory action of blood vessels, maturation and remodeling (Cell, 1996, Vol. 87, pp. 1171-1180; Genes Dev., 1994, Vol. 8, pp. 1897-1909; Science, 1999, Vol. 286, pp. 2511-2514; and Nat. Struct. Biol., 2003, Vol. 10, pp. 38-44). Further, it has also been known that Ang-1 exerts vasodilating and blood flow-enhancing actions by the production of nitric oxide through Tie2 activation (Pharmacol. Res., 2014, Vol. 80, pp. 43-51). In addition, it is believed that Ang-1 contributes to the stabilization of blood vessels by inhibiting the internalization of vascular endothelial cadherin through Tie2 activation (Dev. Cell, 2008, Vol. 14, pp. 25-36). On the other hand, it is believed that Ang-2 is capable of activating Tie2 on vascular endothelial cells, but its activation is believed to be partial, as compared to Ang-1 (Mol. Cell Biol., 2009, Vol. 29, pp. 2011-2022). Ang-2 binds to the same site of Tie2 with substantially the same affinity as Ang-1, and as a result, it has been suggested that Ang-2 functions as an endogenous Tie2 antagonist from the viewpoint that the activation of Tie2 by Ang-1 is replaced by partial activation of Ang-2 (Science, 1997, Vol. 277, pp. 55-60).
An increase in the concentration of Ang-2 in the blood has been reported in a disease induced by vascular vulnerability which is considered to be one of the causes of the disease, such as diabetes, diabetic retinopathy, sepsis, and acute renal failure (Atherosclerosis, 2005, Vol. 180, pp. 113-118; Br. J. Ophthalmol., 2004, Vol. 88, pp. 1543-1546; Critical Care, 2009, Vol. 13, p. 207; and Intensive Care Med., 2010, Vol. 36, pp. 462-470).
Regarding relevance to diabetic retinopathy and diabetic macular edema, it has been reported that the concentration of Ang-2 in the blood plasma or the vitreous humor of patients has risen (Br. J. Ophthalmol., 2004, Vol. 88, pp. 1543-1546; and Br. J. Ophthalmol., 2005, Vol. 89, pp. 480-483). Further, in the retinal blood vessel of patients with diabetic retinopathy, the loss of pericytes which are the main Ang-1 producing cells (Cell, 1996, Vol. 87, pp. 1161-1169) has also been known to be one of the characteristic lesions (Retina, 2013, Fifth edition, pp. 925-939). Diabetic macular edema is known for involving the thickening of the macular area as one of the conditions thereof, but it has also been reported that in patients with an increase in the intraocular Ang-1 concentration due to vitreous removal surgery, the thickening of the macular area is decreased (Br. J. Ophthalmol., 2005, Vol. 89, pp. 480-483). Further, from the viewpoints that in retinal edema mouse models with the loss of pericytes in the retinal blood vessels, retinal edema and retinal bleeding are observed, and the pathology onset is inhibited by the intravitreal administration of Ang-1 (J. Clin. Invest., 2002, Vol. 110, pp. 1619-1628), and that in a test using a mouse model with diabetic retinopathy, vascular endothelial cell disorders in the retina are inhibited by the administration of an adenovirus containing a gene encoding Ang-1 (Am. J. Pathol., 2002, Vol. 160, pp. 1683-1693), it has been suggested that Ang-1 has an action of improving the conditions. Meanwhile, it has been reported that in genetically modified mice having Ang-2 specifically over-expressed in the retina, retinal cell damage is increased (Acta. Diabetol. 2010, Vol. 47, pp. 59-64).
It has been reported that with regard to critical limb ischemia, the amount of Ang-2 in the blood plasma increases in patients with peripheral arterial diseases, and the amount of Ang-2 expressed in the ischemic limb muscles or the skin tissues in patients with critical limb ischemia is high (J. Am. Coll. Cardial., 2008, Vol. 52, pp. 387-393; and Int. Angiol., 2011, Vol. 30, pp. 25-34). Moreover, in a test using a rat model with hindlimb ischemia, blood flow recovery and anti-apoptotic effect in the ischemic limb is promoted by the administration of a viral vector containing a gene encoding Ang-1 (Angiogenesis, 2009, Vol. 12, pp. 243-249). From the viewpoint that it has been reported that mature blood vessels covered by the smooth muscle cells are increased in the border zone of infarcted area by the administration of a virus containing a gene encoding Ang-1 in a coronary artery ligation model of a db/db mouse as an animal model with type 2 diabetes (Diabetes, 2008, Vol. 57, pp. 3335-3343), an effect of promoting the maturation of unstable neovascular vessels can be expected by the activation of Tie2 signals.
As an antibody showing an agonistic action on a human Tie2, a murine monoclonal antibody 15B8 (Patent Document 1) has been reported. It has been reported that 15B8 binds to the human Tie2 to induce an anti-apoptotic action in a human vascular endothelial cell HUVEC (Patent Document 1)